Many types of inflators have been disclosed in the art for inflating an air bag for use in an inflatable restraint system. One type involves the utilization of a quantity of stored compressed gas which is selectively released to inflate the air bag. Another type derives a gas source from a combustible gas generating material which, upon ignition, generates a quantity of gas sufficient to inflate the air bag. In a third type, the air bag inflating gas results from the combination of a stored compressed gas and the combustion products of a gas generating material. The last mentioned type is commonly referred to as an augmented gas or hybrid inflator.
Hybrid inflators that have been proposed heretofore are subject to certain disadvantages. They require glass-to-metal seals or other complex sealing methods to maintain the high pressure seal and/or require an actuation means (mechanical or pyrotechnic) to open the flow passages to the air bag. Many hybrid inflator arrangements dispense cold inflating gas followed by heated gas ("S" curve). This is a disadvantage for an air bag driver system. Additionally, end diffusers typically used on hybrid inflators make packaging in modules difficult.
Thus, there is a need and a demand for improvement in hybrid inflators to the end of overcoming the foregoing disadvantages. The present invention was devised to fill the gap that has existed in the art in these respects.
Additionally, in hybrid inflators and other inflators involving the combustion of a gas generating material, the burning of the pyrotechnic (gas generating) and initiation materials invariably results in the undesired production of particulate material. Various approaches have been attempted and/or suggested to deal with such particulate-containing inflator emissions.
One approach has been to simply inflate the air bag with the particulate-containing inflator emission. As a result, particulate material can be vented out from the air bag and into the vehicle. The particulate material is variously sized and typically includes a large amount of material within the respirable range for humans and can potentially cause consequent respiratory discomfort to humans who have respired the particulate. Also, such particulate can easily become dispersed and airborne so as to appear to be smoke and thereby result in the false impression that there is a fire in or about the vehicle.
It has also been proposed to screen the gaseous emission coming from the pyrotechnic portion of such hybrid inflators. For example, U.S. Pat. No. 5,131,680 discloses the inclusion of a circular screen "128" between the body of pyrotechnic material and the orifice through which the pyrotechnically produced emission is passed to the pressurized gas-containing chamber of the hybrid inflator.
Also, U.S. Pat. No. 5,016,914 discloses the inclusion of a filter identified as a metal disk having a plurality of suitably sized openings therein. The disk is disclosed as functioning to trap large particles such as may be present in the generated gas.
Such techniques of filtering or screening the gaseous emission of the pyrotechnic section of the hybrid inflator prior to contact with the stored, pressurized gas of the inflator generally suffer such as from undesirably slowing or preventing the transfer of heat to the stored gas from the relatively hot generated gas and particulate material. In general, such a transfer of heat to the stored gas is desired in hybrid inflators in order to produce desired expansion of the gas. Consequently, the slowing or preventing of desired heat transfer can result in a reduction in the performance of the inflator. Also, the screening or filtering of particulate at the gas exit port of the pyrotechnic chamber can undesirably effect gas flow within the inflator. For example, such treatment can undesirably restrict the flow of gas out of the pyrotechnic chamber, causing the pressure inside the pyrotechnic chamber to increase and thereby increase the potential for structural failure of the pyrotechnic chamber.
The above-identified U.S. Pat. No. 5,016,914 also discloses constraining gas flow to a tortuous path whereby additional quantities of relatively large particles produced by combustion of the gas generating material are separated from the commingled gases as the gases flow toward the inflatable vehicle occupant restraint. As disclosed, various component parts of the vehicle occupant restraint system cooperate to form the described tortuous path. These component parts include the openings in the container which direct the gas into an outer cylindrical diffuser, the container itself which preferably contains gas directing blades positioned therein as well as burst disks to control the flow of the gas generated by ignition of the gas generating material. The patent also discloses that in a preferred embodiment, a coating material, for example, a silicone grease, is coated onto the inner surface of the container to assist in the fusing of particles thereto rather than allowing the particles to rebound into the nitrogen gas jet stream.
Such surface coatings, however, generally suffer in several significant aspects with respect to effectiveness and functioning when compared, for example, to the use of a filter to effect particulate removal.
First, as the nature of such fusion of adhesion of particles onto a coating is a surface phenomenon, the effectiveness of such removal is directly related to the amount of available surface area. In practice, such a surface coating provides a relatively limited amount of contact surface area and, further, the effectiveness of such surface treatment typically is decreased as the available surface area is occupied.
Also, though such an internal surface coating may be of some use in the fusing of solid particles, such a coating would normally be relatively ineffective in trapping liquid phase particles. Furthermore, the process of condensation of liquid phase particles in an inflator normally involves a transfer of heat to the subject contact surface. In the case of such a surface coated with such a grease, such a transfer of heat could undesirably result in the off-gassing of the coating material, for example, production of gaseous byproducts of the coating material, which in turn would undesirably contribute to the toxicity of the gases emitted from such an inflator.
In addition, the effect of the flow of gases within the inflator can raise concerns about the use of inflators which utilize such coatings. For example, the impingement onto such a coating of the hot combustion gases produced within an inflator would normally tend to displace the coating material, particularly since such coatings tend to become softer at elevated temperatures.
Thus, even for the short time periods associated with the operation of such devices neither exclusive nor primary reliance is made by this patent on the use of such a coating to effect particle removal.
There is a continuing need for a safe, simple and effective, economical apparatus and technique for particulate removal from the gaseous emission of such inflators. The removal of such particulate material can prevent, minimize or reduce any discomfort to which a vehicle occupant may be subjected to as a result of the use of such inflators in the system. Furthermore, such particulate removal can prevent safety concerns such as a vehicle occupant unnecessarily panicking when he or she, seeing particulate material having become dispersed and airborne within the vehicle, arrives at the false conclusion that the vehicle is on fire.